title: Amplified inhibition of stellate cell activation pathways by PPAR-γ, RAR and RXR agonists.
abstract: Peroxisome proliferator activator receptors (PPAR) ligands such as 15-Δ12,13-prostaglandin L(2) [PJ] and all trans retinoic acid (ATRA) have been shown to inhibit the development of liver fibrosis. The role of ligands of retinoic X receptor (RXR) and its ligand, 9-cis, is less clear. The purpose of this study was to investigate the effects of combined treatment of the three ligends, PJ, ATRA and 9-cis, on key events during liver fibrosis in rat primary hepatic stellate cells (HSCs). We found that the anti-proliferative effect of the combined treatment of PJ, ATRA and 9-cis on HSCs was additive. Further experiments revealed that this inhibition was due to cell cycle arrest at the G0/G1 phase as demonstrated by FACS analysis. In addition, the combined treatment reduced cyclin D1 expression and increased p21 and p27 protein levels. Furthermore, we found that the three ligands down regulated the phosphorylation of mTOR and p70(S6K). The activation of HSCs was also inhibited by the three ligands as shown by inhibition of vitamin A lipid droplets depletion from HSCs. Studies using real time PCR and western blot analysis showed marked inhibition of collagen Iα1 and αSMA by the combination of the three ligands. These findings suggest that the combined use of PJ, ATRA and 9-cis causes inhibition of cell proliferation by cell cycle arrest and down-regulation of fibrotic markers to a greater extent compared to each of the ligands alone.
authors.affiliation: Institute of Gastroenterology and Liver Diseases, Tel Aviv Sourasky Medical Center, and Sackler Faculty of Medicine, Tel Aviv, Israel ; Pediatric Gastroenterology Unit, Dana Children's Hospital, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel ; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Efrat
authors.initials: E
authors.lastname: Sharvit
authors.forename: Shirley
authors.initials: S
authors.lastname: Abramovitch
authors.forename: Shimon
authors.initials: S
authors.lastname: Reif
authors.forename: Rafael
authors.initials: R
authors.lastname: Bruck
mesh_terms: D000199:Actins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000077556:Alitretinoin; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D024042:Collagen Type I / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D019938:Cyclin D1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D004357:Drug Synergism; D016193:G1 Phase / Q000187:drug effects / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects*; D055166:Hepatic Stellate Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D008297:Male; D047495:PPAR gamma / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D061251:Primary Cell Culture; D015230:Prostaglandin D2 / Q000031:analogs & derivatives* / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018168:Receptors, Retinoic Acid / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D047488:Retinoid X Receptors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology*; D020741:rho GTP-Binding Proteins / Q000819:agonists / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D000077556:Alitretinoin; D024042:Collagen Type I; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D047495:PPAR gamma; D015230:Prostaglandin D2; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D014212:Tretinoin; D020741:rho GTP-Binding Proteins; C097240:15-deoxy-delta(12,14)-prostaglandin J2; C498862:Acta2 protein, rat; C546845:mTOR protein, rat